Method of and apparatus for circulating liquid metals in fused salt electrolysis

ABSTRACT

A METHOD OF AND AN APPARATUS FOR CIRCULATING A LIQUID METAL IN FUSED SALT ELECTROLYSIS COMPRISING PASSING THE FUSE ALLOY OF THE CATHODE LIQUID METAL AND THE ELECTROLYTICALLY LIBERATED METAL BOTH COMING OUT OF THE CELL AND THE LIQUID METAL FOR CNTROLLING THE TEMPERATURE OF THE CELL THROUGH A LIFT PIPE BY MAKING A MIXTURE OF AN INERT GAS AND THE LIQUID METALS BY THE JETTING FORCE OF THE GAS, SAID MIXTURE BEING SMALL IN SPECIFIC GRAVITY, LIFTING SAID LIQUID METALS INTO A HEAD TANK POSITIONED AT A LEVEL HIGH ENOUGH FOR RECIRCULATING THE LIQUID METALS, INTO THE ELECTROLYTIC CELL BY GRAVITY, SEPARATING THE LIQUID METALS FROM THE INERT GAS IN SAID HEAD TANK, RECIRCULATING THE LIQUID METAL NECESSARY FOR ELECTROLYSIS INTO THE CELL, CONDENSING AND SEPARATING THE ELECTROLYTICALLY LIBERATED METAL CONTAINED IN THE INERT GAS FROM THE GAS, AND RETURNING THE INERT GAS INTO THE LIFT PIPE FOR FURTHER USE BY CIRCULATION.

A ril 17, 1973 HIDETAMI SAKAI ETAL 3,728,234

METHOD OF AND APPARATUS FOR CIRCULJATING LIQUID METALS IN FUSED SALT ELECTROLYSIS Original'Filed March 10, 1970 us. or. 204-68 3 Claims ABSTRACT OF THE DISCLOSURE A method of and an apparatus for circulating a liquid metal in fused salt electrolysis comprising passing the fused alloy of the cathode liquid metal and the electrolytically liberated metal both coming out of the cell and the liquid metal for controlling the temperature of the cell through a lift pipe by making a mixture of an inert gas and the liquid metals by the jetting force of the gas, said mixture being small in specific gravity, lifting said liquid metals into a head tank positioned at a level high enough for recirculating the liquid metals into the electrolytic cell by gravity, separating the liquid metals from the inert gas in said head tank, recirculating the liquid metal necessary for electrolysis into the cell, condensing and separating the electrolytically liberated metal contained in the inert gas from the gas, and returning the inert gas into the lift pipe for further use by circulation.

This is a divisional of application Ser. No. 18,103 filed Mar. 10, 1970, now US. Pat. No. 3,642,603.

BACKGROUND OF THE INVENTION In the method of producing an alkali metal and an alkaline earth metal with a conventional fused salt electrolytic equipment the fused alloy of the cathode liquid metal and the electrolytically liberated metal is distilled and separated and the liquid metal is recirculated into the electrolytic cell to be used as the cathode. In this circulating line a mechanically circulating pump'is employed. In some case, the electrolytic cell is provided with a flow passage at a side or at the bottom thereof through which a liquid metal is passed as the medium for heat to control the temperature of the cell so that the conditions of electrolysis can be stabilized. In the circulating line, too, a mechanically circulating pump is employed.

The electrolysis of fused salt is operated at a considerably high temperature. The alloy of the cathode liquid metal and the electrolytically liberated metal both coming out of the cell and the metal for controlling the temperature of the cell must be circulated to each process of the equipment at high temperatures. However, there are various troubles about the circulation of the liquid metals at high temperatures. For instance, there are the problems of corrosion of the materials of the equipment with the liquid metal, the alloy of the liquid metal and the liberated metal, and the temperature controlling circulating liquid metal, the heat resistance of the equipment itself, and the heat insulation of the high temperature equipment. Also the mechanically circulating pump such as an electromagnetic pump or a centrifugal pump is liable, to get troubles at its shaft seal and other parts. Especially, the complexity of the construction of the equipment increases the possibility of troubles and it is often difficult to secure the safety of operation. All these undesirable factors cause the service life of the equipment to be shortened and the cost of fused salt electrolysis to be raised.

United States Patent 3,728,234 Patented Apr. 17, 1973 SUMMARY OF THE INVENTION The present invention mainly comprises circulating the liquid metal into fused salt electrolytic cell in which a fused metal is used as the cathode by the jetting force of an inert gas instead of using a mechanically circulating pump in the liquid metal circulating line. This method of circulating the liquid metal simplifies the construction of the equipment, facilitates the selection of heat resistant materials and heat insulating materials, and assures the safety of operation, thus resulting in many advantageous effects.

More specifically, this invention provides a method of and an apparatus for circulating the liquid metal into said fused salt electrolytic cell comprising passing the fused alloy of the cathode liquid metal and the electrolytically liberated metal produced in the gap between the cathode and anode through the lift pipe together with the inert gas by the jetting force of the gas, making a mixture of the alloy and the inert gas in the lift pipe by the jetting force of the gas, said mixture being small in specific gravity, transporting the electrolytically liberated metal vapor alone into the inert gas in said lift pipe lifting said mixture into the head tank, separating the cathode liquid metal from the inert gas containing the electrolytically liberated metal in the head tank, condensing and separating the electrolytically liberated metal from the inert gas, cooling, compressing and circulating the inert gas for repeated use, and returning the liquid metal remaining on the bottom of said head tank to the electrolytic cell for re-use.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows diagramatically the circulating line of a fused salt electrolytic equipment suitable for carrying out the method of the present invention.

FIG. 2 shows diagramatically the circulation device for the alloy of fused metals and the temperature controlling liquid metal in the electrolytic cell for the fused salt electrolytic equipment.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, the electrolytic cell 1 is heated by the heater 22. The receiver 2 for receiving the alloy produced by electrolysis is also heated by the heater 23. 3 is the lift pipe standing upright in said receiver 2, 4 the head tank, 5 the condenser, 6 the heat exchanger also serving as gas cooler, and 7 the gas compressor, respectively. The alloy 10 of the cathode liquidmetal 8 and the electrolytically liberated metal 20 produced by electrolysis in the gap between said cathode liquid metal 8 and the anode 9 made of graphite for instance in the electrolytic cell 1 enters the receiver 2 placed at a level lower than that of the cathode liquid metal 8 through the pipe 11. In the receiver 2 is standing the lift pipe 3. The

lift pipe 3 has a length equal to the sum of the height of that part of the receiver 2 which is immersed in the alloy 10 contained therein and the length of the part lifting the alloy 10. Said length of the lift pipe 10 should be such that when the lift pipe 3 is planted upright in the receiver 2 the upper end of said lift pipe 3 will come to a level at least higher than that of the cathode liquid metal 8 in the electrolytic cell 1. In other words, since the lift pipe needs to have a head large enough to return the alloy 10 to the electrolytic cell 1, it should have a length equal to the sum of a length a little greater than the height of the level of said cathode liquid metal 8 and an optional length added. Immediately below the lift pipe 3 is provided the nozzle 13 of the inner gas conduit 12, and when a suitable volume of the inert gas 14 is jetted out at said nozzle 13 into the liquid alloy 10 the mixture 15 of the alloy 10 and the inert gas 14 is produced in the lift pipe 3. This mixture 15 is smaller than the alloy 10in specific gravity. The buoyancy created by the difference in specific gravity and the jetting force of said inert gas 14 combine to serve as a driving force to lift the mixture 15 through the lift pipe 3 into the head tank 4 provided at the upper end of said lift pipe 3. At the same time the electrolytically liberated metal 20 alone has its vapor transported into the inert gas 14 by the effect of the pressure at its temperature. The liquid metal 8 is separated from the inert gas 14 containing the liberated metal 20 in the head tank 4. The inert gas 14 containing the liberated metal 20 is introduced into the condenser 5 through the pipe 17 connected to the upper part of the head tank 4, and the liberated metal 20 is condensed and separated from the inert gas 14 in said condenser 5 and then taken out at the discharge pipe 25. On the other hand, the separated inert gas 14 is transported into the heat exchanger/ gas cooler 6 through the pipe 18 and cooled there to a suitable temperature. Then it is conveyed further to the compressor 7 through the pipe 19 to be made into compressed inert gas 14 and finally blown into said lift pipe 3 through the pipe 12 for recirculation. The liquid metal 8 left behind in the head tank 4 flows down by gravity into the electrolytic cell 1 as the cathode liquid metal 8 for recirculation through the pipe 24 connected to a side of the head tank 4 at a level lower than the upper end of the lift pipe 3.

In the case where'the vapor pressure of the alloy 10 of the cathode liquid metal 8 and the electrolytically liberated metal 20 is low, the separation of the liberated metal 20 from the inert gas 14 containing the liquid metal 8 is facilitated by heating said alloy 10 by the heater 23 provided under the receiver 2. If the inert gas 14 coming out of the compressor 7 is passed into the gas cooler 6 for heat exchange and blown into the nozzle 13 in a warmed state, the heat may be economized. In the condenser 5 the inert gas 14 is cooled to the degree that the liberated metal 20 can be taken out at a temperature a little higher than the melting point of said liberated metal 20. As the liberated metal 20 thus condensed and separated generally contains slight quantities of the cathode liquid metal 8, it is advisable to rectify the liberated metal 20 by a rectifier (not shown) to obtain high purity liberated metal 20. It is possible to produce compounds of the liberated metal 20 by adding other metals directly to the inert gas 14 containing the liberted metal vapor 20.

This equipment can not only lift the alloy 10 in the receiver 2 to required height through the lift pipe 3 by the jetting force of the inert gas 14 but also make a mixture 15 of the alloy 10 and the inert gas 14 by said jetting force and transport only the liberated metal vapor into the inert gas 14 to separate the liberated metal 20- from the cathode liquid metal 8 without resorting to distillation.

The cathode liquid metal used in the present invention may be lead, tin, bismuth, or alloy of two or more of these, the fused salt may be a halide of any of alkali metals or alkaline earth metals or a combination of these, and the inert gas may be argon or nitrogen.

Now an embodiment of this invention will be described in detail by referring to FIG. 1. In the fused sodium chloride electrolytic equipment employing fused lead as cathode, the horizontal electrolytic cell 1 has a metal bottom plate and corrosion resisting brick-lined side plates. Fused lead and fused sodium chloride are introduced into this electrolytic cell 1, and said sodium chloride is electrolyzed at a temperature of 850 C. to produce a lead alloy 10 containing about 10 percent by weight of sodium. Said alloy is introduced into the receiver 2 150 mm. inside diameter and 1,500 mm. high, in which stands said lift pipe mm. in inside diameter and 3,000 mm. long. Said head tank 800 mm.-by-800 mm. square and 1,500 mm. high is installed with its bottom at a level 300 mm. below the top of said lift pipe 3. The lower end 21 of 4 I said lift pipe 3 is open in the shape of a funnel, 100 mm. below which is arranged the 'pipe 12' having said'nozzl'e 12 mm. in inside diameter for blowing out nitrogen gas. When the nitrogen gas is jetted out at this nozzle at a pressure of about 1.4 kg/cm? g. and at a rate of 1.0 liter/second, the fused lead is lifted into the head tank 4 at a rate of 0.11 liter/second. By cooling the nitrogen gas containing the sodium vapor to 350 C. in the condenser 5, we obtained 1.17 kg./hour of sodium. The nitrogen gas was cooled to 50C. in the gas cooler 6, compressed at 2 kg/cm? g. in the oil-free compressor 7, and recirculated. The fused lead in the head tank 4 was returned to the electrolytic cell 1 for recirculation. In case the capacity of the lift pipe to lift the fused lead is large for the electrolyzing capacity of the cell, part of the fused lead can be conveniently circulated between the receiver 2 and the tank 4.

FIG. 2 shows a flow sheet of the said equipment installed together with a device for circulating a liquid metal for controlling the temperature of the electrolytic cell. The cathode liquid metal, fused salt and inert gas used in this embodiment are the same as those used for p the previous one. is' the electrolytic cell provided at its bottom with the flow passage 31 for passing the temperature controlling liquid metal and with the heating section 74. 32 is the receiver for receiving the liquid metal remaining in the distiller, said receiver 32 having the heating section 75. 33 is the receiver for receiving the liquid metal for controlling the temperature of said electrolytic cell 30, said receiver 33 having the heating section 76. 34 and 35 are the lift pipes each planted in the receivers 32 and 33, 36 and 37 the head tanks,

38, 39, 40 and 41 the inert gas coolers, 42 the gas supplying compressor, and 43 the heat exchanger for the liquid metal, respectively. The circulating line for the alloy 46 of the cathode liquid metal 44 and the electrolytically liberated metal produced by electrolysis in the gap between cathode liquid metal 44 and the anode 45 in the electrolytic cell 30 is the same as that for the previous embodiment. Namely, the alloy 46 is introduced into the receiver 32 through the conduit 47. The receiver 32 is so installed that the level of the liquid metal 48 contained in said receiver 32 will come to a level lower than that of the liquid metal remaining on the bottomof the cell 30. In the receiver 32 is planted the lift pipe 34, the upper end of which should come to an optional level higher than that of the cathode liquid metal 44. The orifice 50 at the lower end of the immersed lift pipe 34 is fronted from below by the nozzle 51 of the conduit 72 coming from the compressor 42. The inert gas 52 jetted out flows into said lift pipe 34 through the orifice 51 and makes a mixture 53 of the liquid metal 48 and the inert gas 52 having small specific gravity. Said mixture 53 rises in the lift pipe 34 by the jetting force of the inert gas 52 and is lifted into the head tank 36 provided above, where the liquid metal 48 and the inert gas 52 are separated from each other by the difference of specific gravity. The liquid metal 48 thus separated in the head tank 36 flows down into the electrolytic cell 30 by gravity through the connecting pipe 55 and is circulated again as the cathode liquid metal 44 to make the alloy with the electrolytically liberated metal.

As for the circulation of temperature controlling liquid metal 56, the temperature controlling liquid metal 56 coming from the bottom plate 57 of the cell 30 or through the outlet 58 of the tunnel-shaped flow passage 31 provided in said bottom plate 57 is introduced into the receiver 33 installed at a level lower than that of said outlet 58. In the receiver 33 is planted the lift pipe 35 as in the case of the above-mentioned receiver 32. The inert gas 52 supplied through the conduit 73' of said compressor 42 is blown at the nozzle 61 into the lift pipe 35 through the orifice at the lower end thereof. The mixture 62 of the liquid metal 56 and the inert gas 52 is lifted into the head tank 36 provided above the lift pipe 35 through said lift pipe 35. The liquid metal 56 separated from the inert gas 52 in said head tank 36 flows down through the pipe 64 connected to the outlet 63 of the head tank 36 and enters the heat exchanger 43. In order that the electrolytic cell 30 containing said liquid metal 44 can be kept at a suitable temperature, said liquid metal 56 heated or cooled in said heat exchanger 43 is discharged from the heat exchanger 43 and flows by gravity into the inlet 70 of the flow passage 31 of the cell 30 and then, after controlling the temperature of the electrolytic cell 30 to a level suitable for electrolysis of the fused salt, returns to the receiver 33 through the pipe 59 for recirculation.

The inert gas 52 used as driving force in the circulating lines of the cathode liquid metal 44 and of the temperature controlling liquid metal '56 is separated in the head tanks 36 and 37 respectively. The metal vapor contained in small quantities in the inert gas 52 is collected and separated in the coolers 38 and 39 installed above the head tanks 36 and 37 respectively to prevent the metal vapor from solidifying and choking the circulating lines. After being made free from the metal vapor the inert gas 52 is further introduced in the coolers 40 and 41 through the pipes 65 and 66 to be cooled to a temperature substantially suitable for giving no troubles to the compressor 42. Then the inert gas 52 is returned to the compressor 42 through the pipes 67 and 68 and compressed to a specified pressure high enough to work as the driving force for circulation. During all this time the operation is carried out with the pressure kept slightly higher than the atmospheric pressure to prevent the entry of air into the inert gas piping. The inert gas 52 at said specified pressure is blown into the lift pipes 34 and 3 through the nozzles 51 and 61 provided below them to circulate the cathode liquid metal and the temperature controlling liquid metal.

In the embodiment shown in FIG. 2 the numerical values are the same as those for the previous one and liquid lead is circulated in the temperature control circulating line. It was possible to stabilize the operational conditions of the electrolytic cell by keeping the temperature of liquid lead at 900 C. at its inlet and at 850 C. at its outlet by means of the heat exchanger 43. The fused salt, therefore, was electrolyzed in a highly stabilized state.

Since both equipment shown in FIG. 1 and FIG. 2 do not need the use of mechanically circulating pumps in the liquid metal circulating lines, no severe conditions of materials or complicated constructions are required of the whole equipment, the design of the equipment is simplified with regard to influences of thermal stress, and no special kind of insulating means are necessary for the piping. For these reasons, relatively low-priced materials may be used, the repair and replacement are easy, the safety of operation is high, and the service life is long.

What We claim is:

1. A method of circulating a liquid metal is fused salt electrolytic equipment comprising making a mixture of the alloy of cathode liquid metal and electrolytically liberated metal coming out of the electrolytic cell and an inert gas by the jetting force of said inert gas, lifting the mixture into a head tank through a lift pipe and separating the liquid metal from the inert gas in said head tank, the liquid metal being returned to the electrolytic cell and the gas being j'etted again into the lift pipe.

2. A method of circulating a liquid metal defined in claim 1, wherein a liquid metal controlling the temperature of the electrolytic cell is circulated by the use of another receiver, lift pipe and head tank, an inert gas being jetted into the lift pipe in the receiver to lift the liquid metal into the head tank together with the inert gas, the liquid metal being flowed into the receiver through the electrolytic cell and the inert gas being jetted again into the lift pipe.

3. A method of circulating a liquid metal defined in claim 1, comprising a separation system wherein the alloy of cathode liquid metal and electrolytically liberated metal produced in the gap between the cathode liquid metal and the anode is passed through the lift pipe together with the inert gas to make a mixture of alloy and gas, only the liberated metal for its vapor pressure being transported from the mixture into the inert gas, the remnant alloy being retuned to the electrolyitc cell for circulation and the inert gas being separately cir culated.

References Cited UNITED STATES PATENTS 1,597,231 8/ 1926 Haynes 204-247 X 3,167,492 l/ 1965 Szechtman 204-68 3,546,021 12/ 1970 Craig 204-242 X 3,616,432 10/ 1971 Day 204-250 X 3,620,942 1 1/ 1971 Day 204-68 JOHN MACK, Primary Examiner 'D. R. VALENTINE, Assistant Examiner US. Cl. xn. 204-220, 237, 246, 247, 250 

